The short answer to the question is NO, you cannot have multiple audio interfaces hooked up to your iPad. At least this is probably not going to work the way that you want. I was hoping to use the iPad to route audio around between the iPad, OP-Z, and OP-1, but alas, it’s not quite meant to be.
In the video I show what happens when you try to do this in AUM, and it is a complete bust, whatever the iPad recognized as the last audio device is the one, and only one, that it will recognize. End of Story.
Here there is at least a tiny bit of hope. If you’re using Audiobus 3, you can at least enable Multiroute Audio, which will allow you to use an audio interface, along with a generic USB audio interface that has a headphone jack. In my case I am using a Hyper Drive HD319B, and with either the OP-1 or the OP-Z connected, with Multiroute Audio enabled I can get either (but not both) of the synthesizers to be seen, and get audio out through the headphone jack on the Hyper Drive.
I was really hoping that this would work better, and I would be able to use the iPad as a mini audio routing hub. Alas this is currently not the case, and who knows if it ever will be. Honestly, if you’re trying to use multiple audio interfaces you’re probably much better off with a computer and running a DAW there, but at least you can get a single interface and a headphone output to work with Audiobus 3.
As I mentioned in the YouTube video, if you are aware of anything else working well or enabling multiple audio interfaces on the iPad please reach out, I’ll definitely check out a few more applications on the iPad, but I suspect they’ll all suffer from the same problem.
Until next time, keep on making music!